Sterilizable bags are known in the art for storing a variety of products under sterile conditions, for example, U.S. Pat. Nos. 4,059,919 and 4,063,383. In some instances, such as in the production of mushroom spawn, the bag must be permeable to allow the mushroom mycelium and spawn ingredients, including the growing medium, to maintain a desired moisture content and to receive oxygen for growth and to expel byproduct carbon dioxide. Presently, mushroom spawn is grown on a sterile substrate medium, such as hydrated grain, for example, wheat, rye, millet, barley straw or the like in bags. The bags are usually made of plastics, such as polyethylene, polypropylene, nylon and the like. The plastic used, e.g., polyethylene, is often weak and tears easily. Also, the porosity of the bag may be easily destroyed if the bag is heat sealed.
Usually, a large area comprising as much as 40%-45% of the bag is permeable to gases and this usually means that the bag does not maintain the desired oxygen and moisture content of the substrate satisfactorily resulting in excess air penetration drying out the hydrated substrate or insufficient air penetration which inhibits growth. Also, a large filter area reduces the view area of the bag. In another bag, a small Tyvek patch is placed in the header space, a void area above the mushroom spawn in the bag requiring vertical storage of the bag. Tyvek a high gas exchange rate with moderate filtration but poor tolerance to temperature above 120.degree. C. needed for sterilization. Often when trying to overcome the deficiencies prior art bags, the proposed construction is complicated and requires large amounts of different specialized materials.
Accordingly, there is a need for a new type of prior art bags.